Researchers report that dopamine, a brain chemical
associated with addiction to cocaine, alcohol, and other drugs, may also play an
important role in obesity.
Dopamine relies upon receptors in the brain to "trigger" feelings of
satisfaction and pleasure. In the February 3 issue of The Lancet, scientists
from the U. S. Department of Energy's Brookhaven National Laboratory in Upton,
N.Y., report that obese individuals have fewer dopamine receptors and may eat
more to try to stimulate the dopamine "pleasure" circuits in their brains.
"An obese individual's actions mimic those of a drug addict," said researcher
Dr. Nora D. Volkow. Previous studies by Brookhaven scientists showed that
dopamine plays an important role in drug addiction; addictive drugs increase the
level of dopamine in the brain and addicts have fewer dopamine receptors.
"We hypothesized that the reason behind the compulsive behavior of those who
overeat may be the same as those who are addicted to drugs -- we were right,"
Dr. Volkow told United Press International.
To prove their theory of obesity as a result of addiction, the researchers
measured the number of dopamine receptors in the brains of ten severely obese
individuals and ten people with an average weight. Subjects were injected with a
radioactive chemical "tag" designed to bind the dopamine receptors in the brain.
Then researchers used a positron emission tomography (PET) camera to scan their
brains to determine the number of receptors in each.
Just as the drug addict's brains showed fewer dopamine receptors in previous
research, so did those in the obese individuals. The study also concluded that
as a person's body mass index -- an indicator of obesity -- increased, the
number of dopamine receptors decreased.
"Our research implies a logical reason as to why obesity occurs," explained lead
scientist Dr. Gene-Jack Wang.
While Dr. Wang speculated that the reason obese people have fewer dopamine
receptors may be because their brains are trying to compensate for chronically
high dopamine levels that trigger chronic overeating, the overall consensus is
that it cannot be determined whether the brain changes detected are a
consequence or cause of obesity.
According to the National Heart, Lung, and Blood Institute, over one-half of all
Americans are overweight or obese -- causing the U.S. to be the fattest nation
on earth. While Brookhaven's research may cause many to blame their minds for
their growing middles, Dr. Volkow says that the study's results should instead
encourage proactive measures to lose unnecessary weight.
"Exercise is one of the best ways to stimulate dopamine pleasure and
satisfaction circuits in the brain," said Dr. Volkow. Medication has also been
shown to alter dopamine levels, but many of these drugs are highly addictive.
"The results from exercise are not only beneficial to overall health, but it
also produces the motivation that an addictive behavior needs for change."